Control circuit for a controlled electro-magnetic valve of an automotive braking system

ABSTRACT

A control circuit for a controllable electric solenoid valve of a brake system of a motor vehicle is described, in which the actual values of a controlled variable (f(t)), e.g., the vehicle deceleration, a wheel slip, a driving speed, an angle of rotation or the like are returned to a predetermined tolerance band. The actual value of the controlled variable is measured continuously and compared with the predetermined tolerance band, which is stored in an EEPROM, for example. If the actual value of the controlled variable leaves the predetermined tolerance band ( 22 ), a correction device ( 15 ) intervenes and returns the actual value to the predetermined tolerance band by increasing or decreasing the trigger current for the solenoid valve ( 1 ).

BACKGROUND INFORMATION

The present invention relates to a controllable electric solenoid valveof a brake system of a motor vehicle according to the preamble of themain claim.

German Patent Application 43 05 488 A1 has already described a controlcircuit for a solenoid valve. With this control circuit, the triggercurrent for the solenoid valve is controlled so that the valve closingbody is braked shortly before being moved from its flow-through positionto its closed position. This yields the result that the solenoid valvecloses with very little noise and thus interfering sound waves are nottransmitted through the brake system to the motor vehicle. The virtuallynoiseless closing is achieved by briefly turning off the trigger currentto support the valve closing body in the end position with a holdingcurrent.

German Patent Application 197 07 960 A1 also describes a method and adevice for regulating the pressure in a wheel brake, a regulator forpressure regulation forming a trigger signal from the pressurerelationships prevailing at the valve arrangement. To improve thequality of regulation for the pressure regulation in the brake circuit,one valve arrangement is provided for pressure buildup and another forpressure reduction. By measuring the actual brake pressure and comparingit with the setpoint pressure, a difference is determined and taken intoaccount with an altered trigger signal. The relationship between thetrigger signal and the pressure relationships is stored as acharacteristic curve for the pressure buildup and/or pressure reduction.

ADVANTAGES OF THE INVENTION

The control circuit according to the present invention for acontrollable electric solenoid valve in a brake position system of amotor vehicle having the characterizing features of the main claim hasthe advantage over the related art that a regulator monitors the actualvalue of the controlled variable in question and optionally takes acorrective measure. It is especially advantageous here that thecontrolled variable for the actual value is always within apredetermined tolerance band. If the actual value leaves thepredetermined tolerance band, a correction device additionallyintervenes, returning the actual value to the range of the toleranceband through an appropriate change in the trigger current of thesolenoid valve. This advantageously yields the result that in a brakesystem, for example, quiet or virtually noiseless closing of thesolenoid valve is achieved, while on the other hand, the brake pressurein the brake circuit is adjustable independently of the function of theregulator.

Advantageous refinements of and improvements on the control circuitcharacterized in the main claim are possible through the measurescharacterized in the dependent claims. It is particularly advantageousthat the correction device is designed to alter the field current as afunction of the closing force of the solenoid valve. Through appropriatecharacteristic curves determined empirically in advance, the closingforce of the valve closing body is adjustable at will and is selected bytaking into account the pressure in the line system, so that the closingbody, for example, does not open when there is an increase in the linepressure due to an altered controlled variable. For example, if acurrent/pressure characteristic curve (I/P characteristic curve) hasbeen stored as the controlled variable, then the control current for acertain pressure value may be obtained to advantage according to thecharacteristic curve. It is also advantageous that to regulate thedriving dynamics or the brake performance of a vehicle, for example, thebraking deceleration, the vehicle speed and/or wheel slip values may beselected as the controlled variable. These controlled variables areneeded in particular for an antilock brake system (ABS) or theElectronic Stability Program (ESP).

It is also advantageous that the correction device forms a brakeintervention measure in combination with Adaptive Cruise Control (ACC),as is also used in combination with a speed regulator, when the setpointvalue for the distance is too low for safety reasons with respect to thedriving speed.

A memory is advantageously provided for storing the characteristiccurves for the controlled variable and/or the tolerance band. A suitablememory is preferably an EEPROM, because this memory does not lose itsinformation even in a power failure.

An advantageous implementation also involves the correction devicehaving a computer which calculates the actual value by using a softwareprogram. Software programs have the great advantage that they are easilymodifiable without requiring complex wiring. In particular, in a motorvehicle having an antilock brake system or a driving dynamics regulator,this yields the advantage that correction of the controlled variable iseasily implementable through a corresponding expansion of the existingcontrol programs.

DRAWING

One embodiment of the present invention is illustrated in the drawingand explained in greater detail in the following description.

FIG. 1 shows an electric solenoid valve in an open flow-throughposition.

FIG. 2 shows an electric solenoid valve in an closed position.

FIG. 3 shows a block diagram.

FIG. 4 shows a diagram.

DESCRIPTION

For a better understanding, FIGS. 1 and 2 show an electric solenoidvalve 1 in which a valve closing body 4 is shown in the opened position(FIG. 1) and in the closed position (FIG. 2). Solenoid valve 1 has avalve body 2 in which valve closing body 4 is situated inside a bore.Valve closing body 4 is designed in the lower part so that a hollowspace is formed between the inside wall of valve body 2 and valveclosing body 4, so that brake fluid is forced into this hollow space inthe case of a brake system, for example. Closing body 4 is sealed at thetop with respect to the inside wall of valve body 2. Closing body 4 isheld in its basic position, preferably in the opened position accordingto FIG. 1, by one or more springs 3. In the upper area, a suitablesolenoid M (not shown in detail) through which a field current flows ismounted on valve body 2. The magnetic force which develops acts on valveclosing body 4 with a magnetizing force F_(Mag) against spring forceF_(F) as indicated by the direction arrows in FIG. 2. Closing forceF_(K) which acts on the spherical cup and with which outlet A is closedis obtained from the difference between magnetizing force F_(Mag) andspring force F_(F). The closing force is controlled by the field currentfor the solenoid, so that the desired movement and holding force forvalve closing body 4 are achieved.

The functioning of the present invention will now be explained ingreater detail on the basis of the embodiment according to FIGS. 3 and4. In the case of control of an electric solenoid valve 1, the essentialproblem occurs that manufacturing tolerances, e.g., the size of theresidual air gap between valve body 2 and the driving magnet,temperature effects, friction effects and wear may lead to differentclosing forces at the same trigger currents for the solenoid. Thetrigger current thus depends not only on the differential pressure overthe valve but also the unwanted side effects mentioned above. Apredetermined current/pressure characteristic curve (I/P characteristiccurve) for triggering valve closing body 4 therefore necessarily leadsto different closing forces F_(K) which may then be compensated throughan increase or decrease in the corresponding control current. However,increasing or decreasing the control current by regulation yields anunwanted time lag which is not desirable with the short reaction timesthat are required. For example, in the case of driving dynamicsregulation, when the vehicle begins to swerve, it must be possible tobrake the corresponding wheel of the vehicle through, if possible, animmediate brake response in order to stabilize the driving condition.Therefore, lengthy reaction times are unacceptable.

Therefore, the implementation according to the present invention asshown in FIG. 4 is based on the fact that controlled variable f(t) whichis to be controlled and/or regulated is measured continuously. In thecase of an antilock brake system (ABS) or a vehicle regulator having anelectronic stability program (ESP), the controlled variable may be thevehicle deceleration, a wheel slip, the driving speed, an angle ofrotation or some other dynamic parameter which determines the drivingresponse. Controlled variable f(t) is preselected as a setpoint value inthe time diagram in FIG. 4. In addition, a tolerance band 22 withinwhich the actual value for controlled variable f(t) may vary is givenfor controlled variable f(t). The tolerance band runs about the setpointvalue, i.e., a setpoint value with a time lag. In normal operationwithin the tolerance band, the normal regulator operates with thedesired comfort and harmonious coordination. Outside the tolerance band,the measure taken to intervene in the regulation is preferably moreforceful and more severe.

The values for controlled variable f(t) and/or tolerance band 22 arestored in a suitable memory, e.g., an EEPROM, in the form of a table, acharacteristic curve or in some other suitable form, and thus they maybe accessed by regulator 11 at any time. Tolerance band 22 may bedetermined empirically or according to a worst case analysis.

In driving operation, regulator 11 according to FIG. 4 attempts toregulate actual value 24 in accordance with the measured systemdeviation so that it is within the given tolerance band 22. According toFIG. 3, regulator 11 determines system deviation 17 continuously andderives a suitable control value for triggering hydraulic system 12, 13from stored tolerance band 22. A hydraulic system 13 then increases thepressure in the brake system, for example, and thus increases thedeceleration of vehicle 14. The actual deceleration is then measured andsystem deviation 17 is again determined from that.

If the actual value for controlled variable f(t) is outside of toleranceband 22 according to the left-hand portion of the diagram in FIG. 4,then a correction device 15 intervenes and returns the actual value 24of the controlled variable to I/P characteristics map 16 by increasingthe trigger current for electric solenoid valve 1, for example. Thenregulator 11 again assumes the triggering of hydraulic system 12, 13 onthe basis of the stored engine characteristics map. With the help ofcorrection device 15 an adaptive correction of the controlcharacteristic is then performed. As an alternative, for example, in theright-hand portion of FIG. 4, a reduction in the trigger current isnecessary because the actual value is below tolerance band 22.

1. A control circuit for a controllable electric solenoid valve of abrake system of a motor vehicle for adjusting a holding force for avalve closing body of the controllable electric solenoid valve, thecontrol circuit comprising: a regulator to predetermine a field currentfor the controllable electric solenoid valve according to a setpointvalue of a predetermined controlled variable and to regulate an actualvalue of the predetermined controlled variable within a predeterminedtolerance band; and a correction device to one of increase and decreasethe field current when the actual value leaves the predeterminedtolerance band for the setpoint value of the predetermined controlledvariables, and to alter the field current as a function of a closingforce of the controllable electric solenoid valve.
 2. The controlcircuit of claim 1, wherein the correction device preselects acurrent/pressure characteristic curve as the predetermined controlledvariable.
 3. The control circuit of claim 1, wherein the correctiondevice is operable to correct an actual value of a braking deceleration.4. The control circuit of claim 1, wherein the correction device isoperable to correct an actual value of a vehicle speed.
 5. The controlcircuit of claim 1, wherein the correction device is operable to correctan actual value of a wheel slip value.
 6. The control circuit of claim1, wherein the correction device is operable to perform a brakeintervention measure in conjunction with adaptive cruise control whenthe actual value drops below a setpoint value for the distance from anobstacle.
 7. The control circuit of claim 1, further comprising: amemory to store correction values for a trigger current as a function ofone of the setpoint value of the controlled variable and thepredetermined tolerance band.
 8. The control circuit of claim 7, whereinthe memory includes an EEPROM memory.
 9. The control circuit of claim 1,wherein the correction device includes a computer to calculate theactual value of the controlled variable by executing a software program.10. The control circuit of claim 1, wherein the correction device isoperable to control at least one of an antilock brake system and anelectronic stability program.
 11. The control circuit of claim 1,wherein: the correction device preselects a current/pressurecharacteristic curve as the predetermined controlled variable; thecorrection device is operable to perform at least one of the following:correct an actual value of a braking deceleration, correct an actualvalue of a vehicle speed, correct an actual value of a wheel slip value,and perform a brake intervention measure in conjunction with adaptivecruise control when the actual value drops below a setpoint value forthe distance from an obstacle.
 12. The control circuit of claim 11,further comprising: a memory to store correction values for a triggercurrent as a function of one of the setpoint value of the controlledvariable and the predetermined tolerance band.
 13. The control circuitof claim 12, wherein the memory includes an EEPROM memory.
 14. Thecontrol circuit of claim 12, wherein the correction device includes acomputer to calculate the actual value of the controlled variable byexecuting a software program.
 15. The control circuit of claim 12,wherein the correction device is operable to control at least one of anantilock brake system and an electronic stability program.
 16. Thecontrol circuit of claim 12, wherein the correction device includes acomputer to calculate the actual value of the controlled variable byexecuting a software program, and the correction device is operable tocontrol at least one of an antilock brake system and an electronicstability program.
 17. The control circuit of claim 11, wherein thecorrection device includes a computer to calculate the actual value ofthe controlled variable by executing a software program.
 18. The controlcircuit of claim 11, wherein the correction device is operable tocontrol at least one of an antilock brake system and an electronicstability program.
 19. The control circuit of claim 11, wherein thecorrection device includes a computer to calculate the actual value ofthe controlled variable by executing a software program, and thecorrection device is operable to control at least one of an antilockbrake system and an electronic stability program.